Field of the Invention
The invention relates to an image processing technique, and more particularly, relates to a method for selecting metering mode and an image capturing device thereof.
Description of Related Art
An auto exposure (AE) mechanism has always been a very important part in the development of digital cameras. How to locate a most suitable exposure value (EV) for different scenes regardless of indoor scenes or outdoor scenes is a primary task for the digital camera to restore captured images.
Traditionally, the digital cameras usually include three different metering methods, which are an average metering mode, a center-weighted average metering mode and a spot metering mode. In a basic algorithm for metering, a full image is first divided into N blocks. After a brightness value of each of the independent blocks is calculated, the brightness value is multiplied by a weight value to which the block belongs. Lastly, a brightness of the image measured by such metering method can be obtained by summing the brightness values from each of the blocks. Accordingly, amount of the brightness to be compensated can be decided in a subsequent exposure compensation.
Different metering modes can result in significant differences under the same scene. For instance, if the average metering mode is used when a user is shooting an outdoor panoramic photo (which includes a sky area), a relatively more complete detail of the sky area can be kept in the exposure compensation because the average metering mode considers the entire frame of the image. However, in the case where the spot metering mode is used, because the spot metering mode considers only the brightness at a center area of the frame, the exposure compensation may enhance further if an object at the central area is not bright enough, leading to over exposure on the sky area which is naturally brighter. In addition, as for most of the digital cameras or cell phones, a suitable metering mode may be selected by the user freely on an interface thereof, or may be fixed to one of the metering modes. Nevertheless, under such usage scenario, the image taken by the user can easily be over exposed or without sufficient brightness.